I am confused. In your example, it is in the blockchain and since you have the ability to spend it, then why would any fork make it so you cant spend it?
The spending transaction isn't in the block chain.
You create transaction A and then create the refund transaction B. B is signed by both parties. A is submitted to the blockchain. B has a locktime of 2 years in the future.
A soft fork happens that makes B unspendable for some reason. Perhaps, it requires signatures signed with the original private keys. In that case, it is impossible for either party to create the new spending transaction.
This has already happened with the P2SH fork. If you happened to create a P2SH output, then it would be unspendable. On the plus side, I assume they actually checked that there were no such outputs when the fork was proposed.
The key point is that a (chain of) timelocked transactions that are spendable now, should also be spendable in the future.